Portable boring bars typically comprise an elongated, cylindrical bar that is journaled for rotation in a frame attachable to a work piece. One class of portable boring bars, identified as a “traveling-head” style, employs a tool carrier that can be controlled to traverse the length of the boring bar. During operation, a first drive member rotates the bar while a second drive member actuates the axial position of the traveling-head tool carrier by means of a lead screw. A cutting tool bit attaches to the tool carrier to facilitate various boring and facing metal working applications.
Traditionally, tool carriers are designed to achieve a minimal clearance fit between the internal bore of the tool carrier and the outer circumference of the boring bar. It is desirable to minimize this clearance to help to provide tool bit stability and to minimize deflection and chatter during machining operations. To achieve this minimized clearance, it is typical to require tight tolerances on the deviation from the ideal sizes of the mating parts of the boring bar and tool carrier as they are manufactured. Frequently, it is necessary to “hand fit” the parts to achieve the desired clearance. In addition to making the parts costly to produce, a limitation of the custom-fitting process is that a given tool carrier becomes dedicated to the boring bar for which it was customized due to manufacturing size variations between various boring bars.
An additional drawback to the traditional tool carrier design is that it is difficult to compensate for wear that may occur over time.